Paper coated with compositions of polymeric materials

ABSTRACT

Improved paper coating compositions may be prepared when the latex used therein comprises a blend of a minor proportion by dry weight basis of a latex of a resinous copolymer with a major proportion by dry weight basis of a latex of a polymer consisting of at least 4 monomer units, namely, a conjugated diolefin and an alkenyl aromatic constituting 90-99.8 percent by weight of the copolymer and a carboxylic acid comonomer together with acrolein or methacrolein constituting 0.2 to 10 weight percent.

Elite Mates atet 1191 Chick et al.

[4 1 Nov. 19, 1974 PAPER COATED WITH COMPOSITIONS OF POLYMERIC MATERIALS [75] Inventors: Orest Nicholas Chick, Sarnia,

Ontario; Graham Neville Means, Petrolia, Ontario, both of Canada [73] Assignee: Polysar Limited-Polysar Limited, Sarnia, Canada [22] Filed: Feb. 13, 1974 [21] App]. No.: 442,200

Related US. Application Data [60] Division of Ser. No. 307,407, Nov. 17, 1972, which is a continuation-in-part of Ser. No. 204,762, Dec. 3, 1971, Pat. No. 3,809,666.

Blance et a1. 117/155 UA Freeman 260/297 W Primary Examiner-Morris Liebman Assistant Examiner-T. DeBenedictis, Sr. Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [5 7] ABSTRACT Improved paper coating compositions may be prepared when the latex used therein comprises a blend of a minor proportion by dry weight basis of a latex of a resinous copolymer with a major proportion by dry weight basis of a latex of a polymer consisting of at least 4 monomer units, namely, a conjugated diolefin and an alkenyl aromatic constituting 9099.8 percent by weight of the copolymer and a carboxylic acid comonomer together with acrolein or methacrolein constituting 0.2 to 10 weight percent.

4 Claims, No Drawings PAPER COATED WITH COMPOSITIONS OF POLYMERIC MATERIALS property requirements of such paper; typical of such changes is the advent of web off-set printing. Many conflicting properties are sought in coated paper intended for such use, for example, good adherence of the coating to the fibres (particularly with the increased speed of printing in the web offset process), good ink receptivity, yet sufficient porosity such as will enable the printed paper to be rapidly dried without blistering.

It is an object of this invention to provide a latex composition for preparing an improved paper coating. Another object is to provide a coated paper having in combination good porosity to permit rapid drying without blistering and resistance to picking during the printing operation. The term picking will be later described herein.

lt has now been found that improved paper coating compositions may be prepared from a latex composition comprising a mixture of: (A) 10-40 parts on a dry weight basis of an aqueous latex of a copolymer prepared from a monomer mixture comprising (1) 30-15 weight percent of an acyclic conjugated diolefin monomer, (2) 70-85 weight percent of a monoolefinically unsaturated copolymerizable monomer free of carbonyl structures and (3) -10 weight percent of an olefinically unsaturated carboxylic acid; (B) 90-60 parts on a dry weight basis of an aqueous latex of a copolymer prepared from a monomer mixture comprising l) 0.1-5 weight percent of an olefinically-unsaturated carboxylic acid, (2) 0.1-5 weight percent of an olefinically unsaturated carbonyl compound, (3) 90-99.8 weight percent of monomers composed of 60-30 parts of an acyclic conjugated diolefin monomer and 40-70 parts of a monoolefinically unsaturated copolymerizable monomer free of carbonyl structures.

The invention also provides an improved coated paper whenever prepared from the latex mixture defined herein.

LATEX A The conjugated diolefin monomer used to prepare the copolymer of latex A is an acyclic diene having from 4 to 8 carbon atoms as a butadiene-l,3, for example, butadienel ,3 isoprene. chloroprene and 2,3-dimethylbutadiene-l ,3, of which butadiene-1,3 is preferred. The monoolefinically-unsaturated copolymerizable compound free of carbonyl structures may be an alkenyl aromatic compound such as a styrene or a substituted sytrene monomer, e.g. alpha-methyl styrene and alpha-chlorostyrene and vinyl toluene with styrene being a particularly useful copolymerizable compound. The benefits to be found within the present concept require that the copolymer of latex A contain 30-15 and preferably 25-20 parts by weight of polymerized diolefin and correspondingly -85 and preferably -80 parts by weight of the carbonyl-free monomer; that is to say, the copolymer of latex A must be resinous in nature yet comprise sufficient of the diene moiety which normally forms rubbery polymers to provide a balance of properties. In a preferred embodiment, the copolymer of latex A further comprises units of an olefinically unsaturated carboxylic acid comonomer in the amount of up to 10 weight percent of the copolymer, usually from 1-5 weight percent. Suitable carboxylic acid monomers include those selected from the groups consisting of (a) unsaturated carboxylic acids containing 3-5 carbon atoms, (b) cinnamic acid, and (c) mixtures of (a) and (b), examples of which are acrylic acid, ethacrylic acid, methacrylic acid, itaconic acid, cinnamic acid and mixtures thereof. When the ethylenically unsaturated carboxylic acid monomer units are present they replace a like amount of the carbonyl structure-free monomer.

LATEX B As to latex B, the conjugated diolefin, the monoolefinically-unsaturated copolymerizable monomer free of carbonyl structures, and the ethylenicallyunsaturated acid monomer used to prepare said latex B are each as defined above for latex A.

The olefinically-unsaturated carbonyl compound of the copolymer of latex B is a monomer having an olefinic group and a carbonyl group represented by the general formula: l-l(R )C C(R C(R 0 where R, is hydrogen or a hydrocarbon radical of 1-6 carbon atoms and R and R are hydrogen atoms or C C alkyl radicals. Representative examples of carbonyl compounds which can be used in this invention are acrolein, a-methyl acrolein, B-methyl acrolein, B-phenyl acrolein, methyl vinyl ketone as well as other alkyl vinyl ketones, and their mixtures. Acrolein is the preferred carbonyl compound.

The copolymer of latex B used in accordance with this invention consists of at least 4 monomer units. The first two monomers, the acyclic conjugated diolefin and the monoolefinically unsaturated carbonyl-free copolymerizable monomer, constitute a major part of the polymer, i.e. 99.8 parts per parts by weight of polymer. The proportion of these two monomeric units may vary between 60-30 of diolefin to 40-70 of carbonyl-free monomer but the carbonyl-free monomer should be present in an amount of at least 40 parts per 100 parts by weight of polymer for use in this invention. The other two monomers of the copolymer of latex B, the carboxylic acid compound and the carbonyl compound, constitute a minor part of the polymer, i.e. a total of 0.2-10 parts per 100 parts by weight of polymer and preferably not more than 6 parts. The amount of carboxylic acid monomer may vary from about 0.1 to 5 percent'by weight of total monomer but preferably is within the range of 1 to 5 percent, more preferably 1 to 3, particularly when the latex is to be used in paper coatings containing starch. The unsaturated carbonyl compound may be employed in an amount from 0.1 to 5 percent by weight of total monomer, although 1 to 5 parts are preferred, more preferably 1 to 3. The proportion of the carboxylic acid monomer to the carbonyl monomer may vary within wide limits but it is preferred to maintain it within the range of 3:1 to 1:3 on weight basis.

The polymerization reaction to prepare each of latices A and B is performed in an aqueous emulsion system employing a free radical initiator such as hydrogen peroxide, an alkali metal or ammonium persulphate, azobisisobutyronitrile or a redox initiator pair comprising a reducing compound and an organic peroxide as is well known in the polymerization art. Usually a fraction of a part per 100 parts monomers of a molecular weight regulator such as an alkyl mercaptan containing 8-22 C atoms or a mixture of such mercaptans is employed in the polymerization. The polymerization is carried out in an acidic aqueous medium using one or more synthetic emulsifiers capable of supporting polymerization in an acidic aqueous medium and capable of maintaining a stable dispersion of the copolymer in both acidic and alkaline mediums; such emulsifiers are known in the art and include various alkyl and alkylaryl sulfonates and polyether sulfates; the amount of emulsifier may vary but is usually about 1 to 3 parts per 100 parts of monomers. Once the acid monomer is incorporated as part of the copolymer, the resulting latex emulsion may be converted to an alkaline pH. The total of the ingredients used in the emulsion polymerization may be added either before the reaction is initiated or part may be incrementally introduced during the reaction. It is preferred to charge initially a portion of the monomer mixture and a portion of the aqueous phase and then add the remainder of these ingredients after the polymerization has been initiated.

The temperature of polymerization may vary as known in the emulsion polymerization art but preferably is between to 80C. The polymerization is usually conducted to a high degree of conversion of monomers to polymer but it may also be convenient to stop the reaction when 40-65 percent latex solids are reached and then remove the excess monomer. For most uses, the pH of each latex is adjusted after polymerization from acid, e.g. a pH of 2-6 to alkaline, e.g. a pH of about 7-1 1.

To prepare the mixture of latices A and B according to this invention, the relative proportion should be chosen so that the mixture contains respectively 10-40 parts of dry weight of latex A and 90-60 parts of dry weight of latex B. Particularly desirable improvements are obtained when the latices are mixed so as to provide weight proportions of -25 to 85-75 of the dry weights of latices A and B respectively. In usual practice, the latices will first be combined and then compounded as for a single latex.

The thus prepared latex blend may be combined with fibers, e.g. cellulosic fibers, asbestos, fiberglas, by any of the conventional methods, shaped if necessary, dried and cured. They are particularly useful in preparing compositions for the production of coated paper. These compositions are aqueous pastes containing between 30 and 70 percent by weight of non-volatile materials such as fillers, adhesives such as starch and proteins e.g. casein and isolated soy protein, polymers, dispersants, buffers and defoamers. The compounding techniques, machinery and processes of paper coating are described in Pigmented Coating Processes for Paper and Board TAPPl Monograph Series No. 28 (1964). The filler is selected from one or more of the conventional fillers such as finely divided clays, calcium sulfo-aluminate, calcium carbonate, alumina, silica, titania, zinc oxide and colorants and is used in amounts from about 1 part to about parts per part of uncompounded dry weight solids in the latex and forming preferably at least 60 percent by weight of the total non-volatile material. A suitable adhesive, e.g. starch is used in an amount of 3 to 30 parts dry weight basis per parts filler. Proteins such as casein and soy protein can be used instead of or in addition to starch. An enzyme-converted starch is preferably used.

The compositions of this invention show excellent binding power and impart improved porosity to the coatings thereby providing this much sought-after combination of properties. If strength is of less concern or a greater strength is obtained than is needed the amount of latex in the coating composition may be reduced, which feature is valued in paper for web off-set printing. The improved porosity permits faster drying of the coated paper without the occurrence of blistermg.

In this specification where the following tests of the coated paper art are referred to, they were performed as follows:

Pick Resistance of Coated Papers This test is a measure of the adhesion of the coating to paper and indicates the maximum speed at which the paper can be printed without breaking the coated sur face. A calendered sheet of paper, conditioned for at least 4 hours at 21C and 50 percent relative humidity, is printed with an ink of known tack (l.P.l. No. 5) under a known pressure (35 Kglcm at different speeds in an I.G.T. (lnstituut voor Grafische Techniek, Amsterdam, Netherlands) printability tester. The speed at which picking first occurs is the pick resistance value.

lnk Absorbency of Coated Papers This test provides a measure of the quantity of ink that is absorbed by the coated paper. A photoelectric testing meter is used to measure the brightness of the coated paper before and after inking with a standard ink applied in a manner well known in the art. The ink absorbency is expressed as the percentage loss in brightness.

Wet Rub Resistance of Coated Papers This test measures the amount of the coating that is removed by wet brushing of the coated paper. A model 503 Taber abraded fitted with a rimmed sample holder and with a badger hair brush in place of the grinding wheel is used in this test. A piece of coated paper wetted with 10 mls of water is brushed for a fixed length of time (e.g. 100 revolutions). The water is collected and then its light transmission is measured and compared to that of the reference water. The wet rub resistance is expressed as the percentage of light transmission.

Gurley Porosity The description of this test is found in the TAPPl Test Method T-460, which was modified as used herein to the extent that a smaller volume (l0ccs) of air was used since an alternate method. of measuring the time interval to sufficient accuracy was made available.

Gloss Determined according to TAPPl Test Method T48OTS-65.

Illustration of the invention is provided by the following Examples:

EXAMPLE 1 A number of latex blends were prepared by mixing two latices, A and B, in the dry weight ratios of /90, /80, /70 and 40/60, respectively. The individual latices were identified by the following characteristics:

The results of ai experiment show that the coating composition of this invention provides a coated paper superior to that prepared with the control latex. The improved porosity is obtained while retaining an acceptably good level of resistance to picking." while the control although having a good level of pick resistance had a poor Gurley porosity value.

"TAELTIT l EXPERIMENTAL Ratio 10/90 20/80 30/70 40/60 Control Pick Resistance 197 196 174 170 193 ftJmin.

lnk Absorbency 19.7 22.1 21.5 20.3 18.4

% loss Wet Rub Resistance 97.5 98.0 96.0 96.5 96.0

Gurley Porosity. 341 302 298 299 465 time (seconds) for 10 ecs. of air to pass Gloss 61.2 62.9 62.8 64.3 59.0

Latex A EXAMPLE 1] Another latex similar to latex B of Example 1 was prei q polymer: compQsmm 53:11: pared but with the butadiene-styrene ratio bemg 43/54. itaconic acid 2.5 30 80 parts of this latex (dry weight basis) was blended i with 20 parts (dry weight basis) of latex A of Exampleemulsifier type: anionic, synthetic (sulfonated fatty acid) 1 and compounded 1n the same way. This coating comp 8.8 pound and the Control compound of Example 1 were applied to a paper substrate at a coating weight of 8 Latex B vpounds per ream. The two coated papers were dried and tested as in Example 1. The results are shown in Polymeric w g i jg wclgh Table 11 and clearly point to the superiority of the latex acyrylic acid 5 composition of this invention. itaconic acid 1.0 acrolein 1.5 40 latex solids. weight /r 49.6 emulsifier type: anionic. synthetic TABLE [I (sulfosuccinatc ester) pH 7.5

Test Experimental Control With each of the above latex blends a paper coating Pick Resistance mm 315 v 255 compositlon was prepared to a total SOllClS of 60 perwktARbsrRbency 10 5 5 13.0 cent by weight from the following formulation: f gsgf i i z g 58d 2? Gloss 7: 58.5 57.0

. Parts by Weight. Paper coating grade china clay 85 5 Precipitated calcium carbonate Oxidized starch 5 Latex 12 The pH of each coating composition was adjusted to 8.8 and each was found to have satisfactory rheology properties when tested on a Hercules Hi-Shear rhet were prepared according to the formulation given in Example 1, the one coating utilizing the 20/80 ratio ometer. With each coating composition a coated paper a was prepared by -applying the composition to an uncoated paper substrate to a coat weight of 4 pounds per ream by means of a laboratory model coating device.

After drying, the coated paper was subjected to testing, 60 a the results of which are shown in Table l. v

Also prepared and tested was paper coated with a; commercial paper-coating latex as a control. This latex had the following properties:

polymer type carboxylated butadienelstyrene copolymer (60'71 styrene) latex solids 50% 9 Another latex similar to latex B of Example 1 wasprejpared but with the acrolein being omitted from the po- EXAMPLE 111 lymerization recipe. Two paper coating compositions latex blend according to Example I, while the other coating utilizinga latex blend of 20 parts of latex A described in Example 1 and parts of the present acrolein-free latex. Each of these coating compositions were applied to paper at a coating weight of 10 pounds per ream and the papers were then dried and tested as before. The results as recorded in Table 111 show clearly .the better properties obtained when polymerized acrolein forms part of the molecular structure of the polymer in latex B, particularly in pick resistance and porosity.

Acrolein-Containing Acrolein-Containing Polymer Present Test Polymer not in Latex in Latex Pick Resistance t't/min 387 426 lnk Absorbcncy 7r loss 13.5 l8.l Wet Rub Resistance 7r 87.0 98.5 Gurley Porosity seconds 6l8 478 Gloss X 79.9 78.l

EXAMPLE lV polymerizable monomer free of carbonyl structures sc- A coated paper was prepared using a 20/80 latex blend similar to that in Example I except that the latex A in the present example was prepared without the use of an unsaturated carboxylic acid monomer. The coating weight was pounds per ream in the present example. The properties of the coated paper were compared with those obtained using a Control as in Example I also applied at 10 pounds per ream.

TABLE IV Test Control Invention Pick Resistance l't/min. 335 35 6 Ink Ahsurhcncy .l loss 12.3 l6.0 Wet Rub Resistance A 95.5 95.0 (iurley Porosity seconds X50 397 (iloss "l 75.l 77.2

These results demonstrate the improved properties obtained by means of the present invention.

What is claimed is:

1. Paper coated with a composition having a pH of 7-1 1 and comprising a latex blend, a filler and an adhesive, said filler being selected from finely divided clay,

olefin monomer selected from butadiene-l,3, isoprene,

chloroprene and 2,3-dimethylbutadiene-l,3, (2) 70-85 weight percent of a monoolefinically unsaturated colected from styrene, alpha-methyl styrene. alphachlorostyrene and vinyl toluene, and (3) 0-l0 weight percent of an olefinically unsaturated carboxylic acid selected from the groups consisting of (a) unsaturated carboxylic acids containing 3-5 carbon atoms, (b) cinnamic acid, and (c) mixtures of (a) and (b); (B) 90-60 parts on a dry weight basis of an aqueous latex of a copolymer prepared from a monomer mixture comprising (1) 0.1-5 weight percent of an olefinically unsaturated carboxylic acid as defined in subsection (A) (3), (2) 0. l-5 weight percent of an olefinically unsaturated carbonyl compound selected from acrolein, alpha-methyl, beta-methyl and beta-phenyl acroleins, methyl vinyl ketone and mixtures thereof, (3) 90-998 weight percent of monomers composed of 60-30 parts of an acyclic conjugated diolefin monomer as defined in subsection (A) (l) and 40-70 parts of a monoolefinically unsaturated copolymerizable monomer free of carbonyl structures as defined in subsection (A) (2).

2. A coated paper according to claim 1 wherein the acyclic conjugated diolefin monomer wherever referred to is butadiene-l ,3 and the monoolefinically unsaturated copolymerizable monomer free of carbonyl structures whereever referred to is styrene.

3. A coated paper according to claim 1 wherein the latex blend comprises a blend of l5-25 parts on a dry weight basis of latex A and 85-75 parts of latex B and wherein the proportions of the monomers used in preparing these latices are as follows: (A) (l) is 25-20, (A) (2) is -80, (A) (3) is l-5, (B) l is l-3, (B) (2) is l-3 and (B) (3) is 94-98.

4. A coated paper according to claim 3 wherein the monomers are as follows: (A) l is butadiene-l .3, (A) (2) is styrene, (A) (3) is itaconie acid, (B) (l is a mixture of acrylic and itaconic acids, (B) (2) is acrolein and (B) (3) is a mixture of butadiene-l,3 and styrene. l l l =l= 

1. PAPER COATED WITH A COMPOSITION HAVING A PH OF 7-11 AND COMPRISING A LATEX BLEND, A FILLER AND AN ADHESIVE, SAID FILLER BEING SELECTED FROM FINELY DIVIDED CLAY, CALCIUM SULFOALUMINATE, CALCIUM CARBONATE, ALUMINA, SILICA, TITANIA, ZINC OXIDE AND COLORANTS AND BEING PRESENT IN AMOUNT OF 1-20 PARTS BY WEIGHT PER PART OF LATEX BLEND (DRY WEIGHT), SAID ADHESIVE BEING SELECTED FROM STARCH, CASEIN AND SOY PROTEIN AND BEING PRESENT IN AMOUNT OF 3-30 PARTS BY WEIGHT PER 100 PARTS BY WEIGHT OF FILLER, SAID LATEX BLEND BEING A BLEND OF (A) 10-40 PARTS ON A DRY WEIGHT BASIS OF AN AQUEOUS LATEX OF A COPOLYMER PREPARED FROM A MONOMER MIXTURE COMPRISING (1) 30-15 WEIGHT PERCENT OF AN ACRYCLIC CONJUGATED DIOLEFIN MONOMER SELECTED FROM BUTADIENE-1,3, ISOPRENE, CHLOROPRENE AND 2,3DIMETHYLBUTADIENE-1,3, (2) 70-85 WEIGHT PERCENT OF A MONOOLEFINICALLY UNSATURATED COPOLYMERIZABLE MONOMER FREE OF CARBONYL STRUCTURES SELECTED FROM STYRENE, ALPHA-METHYL STYRENE, ALPHA-CHLOROSTYRENE AND VINYL TOLUENE, AND (3) 0-10 WEIGHT PERCENT OF AN OLEFINICALLY UNSATURATED CARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF 8A) UNSATURATED CARBOXYLIC ACIDS CONTAINING 3-5 CARBON ATOMS, (B) CINNAMIC ACID, AND (C) MIXTURES OF 8A) AND (B): (B) 90-60 PARTS ON A DRY WEIGHT BASIS OF AN AQUEOUS LATEX OF A COPOLYMER PREPARED FROM A MONOMER MIXTURE COMPRISING (1) 0.1-5 WEIGHT PERCENT OF AN OLEFINICALLY UNSATURATED CARBOXYLIC ACID AS DEFINED IN SUBSECTION (A) (3), (2) 0.1-5 WEIGHT PERCENT OF AN OLEFINICALLY UNSATURATED CARBONYL COMPOUND SELECTED FROM ACROLEIN, ALPHAMETHYL, BETA-METHYL AND BETA-PHENYL ACROLEINS, METHYL VINYL KETONE AND MIXTURES THEREOF, (3) 90-99.8 WEIGHT PERCENT OF MONOMERS COMPOSED OF 60-30 PARTS OF AN ACYCLIC CONJUGATED DIOLEFIN MONOMER AS DEFINED IN SUBSECTION (A) (1) AND 40-70 PARTS OF A MONOOLEFINICALLY UNSATURATED COPOLYMERIZABLE MONOMER FREE OF CARBONYL STURACTURES AS DEFINED IN SUBSECTION (A) (2).
 2. A coated paper according to claim 1 wherein the acyclic conjugated diolefin monomer wherever referred to is butadiene-1,3 and the monoolefinically unsaturated copolymerizable monomer free of carbonyl structures whereever referred to is styrene.
 3. A coated paper according to claim 1 wherein the latex blend comprises a blend of 15-25 parts on a dry weight basis of latex A and 85-75 parts of latex B and wherein the proportions of the monomers used in preparing these latices are as follows: (A) (1) is 25-20, (A) (2) is 75-80, (A) (3) is 1-5, (B) (1) is 1-3, (B) (2) is 1-3 and (B) (3) is 94-98.
 4. A coated paper according to claim 3 wherein the monomers are as follows: (A) (1) is butadiene-1,3, (A) (2) is styrene, (A) (3) is itaconic acid, (B) (1) is a mixture of acrylic and itaconic acids, (B) (2) is acrolein and (B) (3) is a mixture of butadiene-1,3 and styrene. 